The present invention relates to blades for the propeller of motorized fans employed in particular in the automobile industry.
Propellers are used in many technical fields and in particular for fans. This is the case in the automobile industry in which motorized fans are associated with cooling radiators of heat engines.
As is known, each blade of a propeller, in particular of a motorized fan unit, produces a slip-stream which rotates at the speed of rotation of the propeller. This slip-stream generates a sound which is intense when it encounters a fixed obstacle. This is for example the case when the slip-stream encounters the arms of supports of a motorized fan unit which support the latter for maintaining it in a fixed position relative to the radiator with which it is associated.
Such axial fans produce a highly turbulent slip-stream which generates considerable noise. Indeed, when the slip-stream of a blade passes in front of a support arm, it produces a mechanical impulse which results in a particular noise which is added to the aerodynamic noise or to the noise of the driving motor.
The interest of reducing the noise produced by such a rotating slip-stream which passes in front of the support arms of the fan will of course be understood if a more silent operation is to be obtained.
The structure of the slip-stream produced by a blade is a function of the aerodynamic definition of the latter and in particular of the evolution of the range of speeds in the passage formed between two neighbouring blades. More specifically, it has been found that these slip-streams may create around the support arms non-stationary systems which are sources of noise if the gap between the trailing edges of the blades and the support arms is relatively small. It has been found that the slip-stream located in the extension of the trailing edges of the blades disappears relatively rapidly at a certain distance in the downstream direction from the trailing edge owing to the damping due to the viscosity of the air and that this slip-stream is then lost in the general turbulence of the flow.
Thus it can be seen that if it is possible to increase the distance between the trailing edge of such a propeller blade and the support arms supporting it without increasing the overall axial size of the assembly, the noise produced by the slip-stream when it encounters the fixing arms or the like may be reduced.